The present invention relates to an optical instrument and a method for obtaining distance and image information of an object.
Optical Instruments, and in particular optical instruments, such as video tachymeters or video total stations, comprise a complex arrangement of optical elements such as lenses of a telescope, a camera and distance measuring means for obtaining information regarding the shape and the location of an object. This information may include horizontal and vertical angles and a distance to the object as well as an image of the object. The information may then be used to create a three-dimensional representation of the object.
However, after acquiring an image with such an optical instrument, the acquisition of three-dimensional data is time consuming. For example, for measuring a three-dimensional grid, the instrument has to sequentially scan by tilting and panning the distance measuring means and measure each position corresponding to a point in the grid, which is time consuming.
To generate a grid, it is desired to obtain a distance measurement for multiple positions corresponding to multiple pixels in an image. However, the correspondence between a pixel taken by the camera and a position to be measured may not be linear so that obtaining the coordinates of the exact position to be measured is difficult and thus distance measurements may vary. Therefore, there is a need for higher accuracy in positioning and distance measurement.
Other optical surveying instruments with imaging, direction and distance measuring capabilities often comprise scanning means for obtaining image, direction and distance information, where a fast rotating polygon mirror for laser beam deflection is used. Specifically, a laser beam of a distance measuring means is scanned over the object, while a distance to a position on the object is measured and the direction, e.g. indicated by horizontal and vertical angles, to the position on the object with respect to the origin or mirror position of the instrument is recorded.
Such instruments are capable of providing images of the object at video rate including distance information of each scanned position on the object. Thereby, multiple data points corresponding to the measured positions may be obtained, wherein each data point may comprises three-dimensional information. Of course, the higher the requirements on the resolution, the more data points need to be obtained, leading to a vast amount of information that has to be processed, which is often only possible offline.
While the above discussed instruments may obtain three-dimensional representations of an object with sufficient resolution for many applications, some applications require still higher resolution and a higher accuracy. Moreover, in the mirror scanning systems, it is not possible to obtain a second distance measurement of the exact same position, since it is not possible to obtain the exact same laser beam deflections on, for example, the rotating polygon mirror twice. Further, since processing of the large amount of data has to be done usually offline back in the office, the operator cannot return to features of interest on site. Thus, although fairly high resolution is obtained for the whole scanning area, this turns into a disadvantage if data corresponding to a few features of interest in the scanned area have to be isolated.